In waterflooding procedures in oil-bearing strata, relatively more permeable zones in the subterranean formation tend to take most of the injected fluids. This may be acceptable initially in sweeping oil from zones of relatively high permeability, but subsequently this tends to become undesirable as the hydrocarbon content of such strata becomes depleted resulting in much of the subsequently injected floodwater or other fluid by-passing the less permeable but still oil-bearing zones and providing little benefit in further hydrocarbon recovery.
Indepth plugging has been effected in the past by the injection of gelable thickened aqueous solutions containing various polymers, either with or followed by the injection of sesquestered polyvalent metal cations, which, on contact with the polymers, cause gelation or crosslinking of the thickened aqueous solutions, thus achieving plugging. The more permeable strata take the injected treating solutions of polymer and injected polyvalent metal cation solutions, and on admixture out in the strata, plugging occurs. This permeability correction then forces subsequent floodwater injections to by-pass the now less permeable subterranean zones, and to push, instead, into the now relatively permeable strata hopefully containing oil to enhance further hydrocarbon recovery.
Variations of the approach have been used in the past, admixing of the polymer and metal cation salt solutions, with or without acid, in various dilutions and using various polymers. It has been a relatively costly procedure. Sequestering agents used have been employed to avoid too rapid a reaction of the polyvalent metal cation compound solutions, to retard their effect somewhat, in order to delay the onset of gelation until the injected solution has penetrated deeper into the subterranean formation. The metal cation compounds themselves are reasonably expensive, and large volumes are required. Yet, no better approach has been developed.